In recent years there has been an extensive development towards using more modern access network technologies in telephony and this also turns out to be a challenge for the traditional circuit switched technology. An example there is the IP telephony, which is taking a growing share of the market. It is also possible to use traditional analog telephones as interfaces against specialized kinds of access networks, by using special telephony equipment that converts the analog signals to a format suitable for such a network. FIG. 1 illustrates this situation, where the analog telephone and the special telephony equipment represent the local network placed in the residential area of the subscriber, and the access network is the telephone operator's equipment outside the residential area.
Most often there is a number of telephony jacks installed in the residential area These jacks are connected in series and there is a first jack that is connected to the traditional Public Switched Telephony Network (PSTN). This is shown in FIG. 2. These serially connected jacks may be called a local telephony network.
If the analog telephones of the local telephony network instead are to be used as interfaces against a modern access network, e.g., a digital network, the signals have to be converted to the format of this network by means of some kind of special telephony equipment, see FIG. 3. A problem to solve is how to use the existing jacks in the residential area together with the special telephony equipment in an optimum way, that is with a least possible change of the jacks and equipment installed.
One non-optimum solution consists in physically cutting the connection to the PSTN and connecting the first jack to the special telephony equipment instead. This is seen in FIG. 4. The problem is that cutting wires to the PSTN and rewiring of the first jack requires professional installation work, resulting in additional costs.